This application relates generally to communication systems, and, more particularly, to wireless communication systems.
Wireless communication systems use a network of access points such as base stations to provide wireless connectivity to various access terminals, such as mobile units, user equipment, or other devices that are enabled for wireless communication. The coverage area of a wireless communication system is typically divided into a number of geographic areas that are conventionally referred to as cells or sectors. The coverage area of each cell in the wireless network is limited by the propagation loss of radio signals transmitted by access points that provide coverage to the cell. Thus, the coverage area of each cell is determined by the location and the transmit power or distribution pattern of the access point, as well as the geography of the cell, the location of any interfering objects, antenna geometry, topology and environmental conditions, shadow fading and the like. For example, the coverage area of a cell may be reduced if a building or a mountain is present near the access point. The boundaries of the cells are not rigidly defined and may vary with time. Thus, coverage areas may overlap such that multiple access points may provide coverage to the overlapping regions, although the strength of the signal provided within the overlapping regions may be different for the different access points. Overlapping coverage areas may help to ensure session transitions for mobile user equipment from one cell to another cell.
Wireless communication standards such as Long Term Evolution (LTE, LTE-Advanced) support broadcasting services such as the multimedia broadcast multicast service (MBMS) or the enhanced multimedia broadcast multicast service (eMBMS). The MBMS services broadcast or multicast data from base stations over the air interface on channels that can be received by one or more users. The eMBMS is an enhanced version of MBMS that provides additional features such as an architecture and physical layer enhancements that allow the eMBMS service to carry multimedia information to user equipment. The eMBMS service can transmit information towards user equipment by broadcasting or multicasting to the user equipment in a multicast broadcast single frequency network (MB-SFN) mode. An SFN is generally understood to be a broadcast network where more than one transmitter simultaneously or concurrently sends the same signal over the same frequency channel. The MB-SFN mode is used to transmit the same information from all of the base stations in a selected group of cells or coverage area. Each of the base stations in the MB-SFN area transmits the same content time-aligned in the same resource blocks of the physical layer. Constructive combination of the signals transmitted by the different base stations in the MB-SFN area enhances the received signal strength and reduces interference within the cells of the MB-SFN area.